Aromatic vs diradical character in the transition states of the cope rearrangements of 1,5-hexadiene and its cyano derivatives

J J  Blavins; D L  Cooper; P B  Karadakov

doi:10.1021/jp036660i

Aromatic vs diradical character in the transition states of the cope rearrangements of 1,5-hexadiene and its cyano derivatives

J J Blavins, D L Cooper, P B Karadakov

Chemistry

Research output: Contribution to journal › Article › peer-review

Abstract

Using geometries optimized at the (U)B3LYP/6-31G(d) level, ab initio modern valence bond calculations are used to quantify directly the relative importance of aromatic, diradical, and bisallyl contributions to the transition states of gas-phase Cope rearrangements of 1,5-hexadiene and various cyano derivatives. The main effect on the character of the transition state of substituting radical-stabilizing cyano groups is found to be indirect, via the geometry, with shorter interallyl separations favoring diradical character and larger ones favoring aromaticity. In the case of the parent Cope reaction, the weights of the aromatic and diradical components are comparable at the transition state. We find that bisallyl character only becomes important for transition states with rather large interallyl separations.

Original language	English
Pages (from-to)	194-202
Number of pages	9
Journal	Journal of Physical Chemistry A
Volume	108
Issue number	1
DOIs	https://doi.org/10.1021/jp036660i
Publication status	Published - 8 Jan 2004

Keywords

AB-INITIO CALCULATIONS
VALENCE-BOND THEORY
REACTION-MECHANISMS
CYCLOBUTADIENE
PERTURBATION

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10.1021/jp036660i

http://dx.doi.org/10.1021/jp036660i

Cite this

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title = "Aromatic vs diradical character in the transition states of the cope rearrangements of 1,5-hexadiene and its cyano derivatives",

abstract = "Using geometries optimized at the (U)B3LYP/6-31G(d) level, ab initio modern valence bond calculations are used to quantify directly the relative importance of aromatic, diradical, and bisallyl contributions to the transition states of gas-phase Cope rearrangements of 1,5-hexadiene and various cyano derivatives. The main effect on the character of the transition state of substituting radical-stabilizing cyano groups is found to be indirect, via the geometry, with shorter interallyl separations favoring diradical character and larger ones favoring aromaticity. In the case of the parent Cope reaction, the weights of the aromatic and diradical components are comparable at the transition state. We find that bisallyl character only becomes important for transition states with rather large interallyl separations.",

keywords = "AB-INITIO CALCULATIONS, VALENCE-BOND THEORY, REACTION-MECHANISMS, CYCLOBUTADIENE, PERTURBATION",

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T1 - Aromatic vs diradical character in the transition states of the cope rearrangements of 1,5-hexadiene and its cyano derivatives

AU - Blavins, J J

AU - Cooper, D L

AU - Karadakov, P B

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Y1 - 2004/1/8

N2 - Using geometries optimized at the (U)B3LYP/6-31G(d) level, ab initio modern valence bond calculations are used to quantify directly the relative importance of aromatic, diradical, and bisallyl contributions to the transition states of gas-phase Cope rearrangements of 1,5-hexadiene and various cyano derivatives. The main effect on the character of the transition state of substituting radical-stabilizing cyano groups is found to be indirect, via the geometry, with shorter interallyl separations favoring diradical character and larger ones favoring aromaticity. In the case of the parent Cope reaction, the weights of the aromatic and diradical components are comparable at the transition state. We find that bisallyl character only becomes important for transition states with rather large interallyl separations.

AB - Using geometries optimized at the (U)B3LYP/6-31G(d) level, ab initio modern valence bond calculations are used to quantify directly the relative importance of aromatic, diradical, and bisallyl contributions to the transition states of gas-phase Cope rearrangements of 1,5-hexadiene and various cyano derivatives. The main effect on the character of the transition state of substituting radical-stabilizing cyano groups is found to be indirect, via the geometry, with shorter interallyl separations favoring diradical character and larger ones favoring aromaticity. In the case of the parent Cope reaction, the weights of the aromatic and diradical components are comparable at the transition state. We find that bisallyl character only becomes important for transition states with rather large interallyl separations.

KW - AB-INITIO CALCULATIONS

KW - VALENCE-BOND THEORY

KW - REACTION-MECHANISMS

KW - CYCLOBUTADIENE

KW - PERTURBATION

U2 - 10.1021/jp036660i

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